Polymer foams are widely used in a variety of cushioning applications. Foams are commonly used in pillows, seating, mattresses and similar applications where softness and comfort are predominating factors. Foams are also used to cushion the contents of a package. In packaging, the foam, typically, only sees moderate strains due to jostling or dropping of the package and as a result is typically only elastically deformed (i.e., the foam springs back after being deformed, which is typically less than about 10% strain). Packaging foam also has little if any requirements related to the dimensions of the foam, but merely must cushion the contents against low impacts. Consequently, it is quite common for inexpensive expanded polystyrene bead foam and expanded cellulose based packaging peanuts to be used even though each of these are susceptible to considerable deformation due to temperature and humidity respectively.
In recent years, automobiles have been required to meet ever more stringent demands for mitigating occupant injury during crashes. To do so, automobiles have incorporated active systems such as air bags for frontal collisions. More recently, more and more attention has been paid to side crashes and head injuries from rollover accidents. These have employed side air bags, inflatable curtains (SABIC's) and have also started to employ foams that absorb energy not merely by elastically deforming, but by inelastically deforming (i.e., being crushed).
The vast majority of the foams used for automobile crash mitigation have been closed cell thermoset foams such as polyurethane/polyurea and their derivatives. These unfortunately, are difficult to recycle and to achieve crash efficiency they need to be friable causing them to possibly deteriorate over time, for example, due to vibration in a vehicle or weathering.
Other foams that have been employed have tended to be closed cell crystalline or semi-crystalline thermoplastic foams such as expanded polypropylene beads and polypropylene coalesced foam strands as described by U.S. Pat. No. 6,213,540. Each of these automobile energy absorbing foams tend to be expensive and of greater weight for the compressive energy absorbed than desired. For efficient absorption of crash energy, the foams have needed to have anisotropic strength due to anisotropic cells as described in U.S. Pat. No. 6,213,540 and US Pat. pub. 2006/0148919. Because of this orientation, these foams have needed to be oriented properly relative to the expected impact direction on the foam to get the expected crash absorption.
Accordingly, it would be desirable to provide an energy absorbing foam for vehicles that is inexpensive, has low weight, good energy absorbance and has uniform efficient crash absorption in multiple impact directions.